The invention relates to a belt tensioner, but more particularly, the invention relates to a spring biased tensioner of the eccentric type wherein the tensioner's effective pivot arm is located within the inside diameter of a bearing.
Eccentric type tensioners may be classified in one of two general categories where in one category, elements in addition to a pivot and a pivot bushing are included within the confines defined by the inside diameter or bore of a pulley bearing. Such tensioners require a large bearing which typically includes the attendant disadvantages of higher costs and larger tensioner size as compared to tensioners having smaller sized pulley bearings. An example of an eccentric type belt tensioner falling in this category, is disclosed in U.S. Pat. No. 4,808,148.
Eccentric type belt tensioners of the second category are those which exclude additional elements other than a pivot-pin and a pivot bushing disposed within the confines of the inside diameter of a pulley bearing member and, because of this, such tensioner may be constructed with a smaller diameter bearing than those of the first category. Consequently, tensioners of the second category may be somewhat smaller than those of the first category. Nevertheless, the bearing of such tensioners may be oversized to accommodate a minimum pivot arm length within the inside diameter of the bearing which results in the bearing being oversized for the load that it must carry. An oversized bearing may result in increasing the necessary size for a tensioner as well as introducing excessive costs. An example of a belt tensioner of the second category is disclosed in U.S. Pat. No. 4,889,520.
The present invention primarily concerns belt tensioners of the latter category and makes possible the use of very small pulley bearings such as those having an inside diameter or bore of less than 25 mm. However, the features of the invention may also be used for tensioners of either category particularly where it is desirable to maximize the eccentricity of the tensioner in terms of pivot arm length.